AN ENGINE KNOCK CONTROL SYSTEM AND A METHOD OF CONTROLLING AN ENGINE KNOCK IN AN ENGINE WITH TURBOCHARGER

Abstract

An engine knock control system for an engine having a turbocharger includes a first module that determines octane scalars indicative of an engine knock propensity for each cylinder of the engine system and a second module that determines a cylinder air mass limit based on the octane scalars. A third module limits a boost output of the turbocharger based on the cylinder air mass limit.

Full Text

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ENGINE KNOCK CONTROL FOR TURBOCHARGED ENGINES
FIELD OF THE INVENTION
[0001] The present invention relates to internal combustion engines,
and more particularly to knock control in a turbocharged engine.
BACKGROUND OF THE INVENTION
[0002] Internal combustions engines combust an air and fuel (A/F)
mixture within cylinders to produce drive torque. More specifically, the
combustion events reciprocally drive pistons that drive a crankshaft to provide
torque output from the engine. The A/F mixture is ignited or sparked at a
desired crank angle. In some instances, however, the A/F mixture ahead of
the flame-front auto-ignites within the cylinder resulting in undesired engine
knock.
[0003] Accordingly, engine knock control systems have been
developed to detect and to mitigate engine knock. One such engine knock
control system is disclosed in U.S. Patent No. 5,560,337, entitled Knock
Control Using Fuzzy Logic, and issued on October 1, 1996. Such traditional
systems detect the propensity for a particular cylinder to auto-ignite and retard
the cylinder spark timing to avoid engine knock. Although engine knock is
avoided, exhaust gas temperatures increase as a result of the retarded spark
timing.
[0004] Some internal combustion engines include a turbocharger,
which increases the charge air density ingested by the engine. The
turbocharger is driven by the exhaust gas, whereby the heat energy of the
exhaust gas is transformed into mechanical energy to compress the air
entering the engine. In turbocharged engines, engine knock will occur at high
loads, especially when a low octane (e.g., 85 octane) fuel is used.
Consequently, a persistent knock condition can occur.

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[0005] Traditional engine knock control systems do not sufficiently
mitigate engine knock when applied in a boosted internal combustion engine.
More specifically, traditional engine knock control systems retard spark in
order to mitigate engine knock. However, spark retard results in higher
exhaust temperatures, which in turn result in increased boost of the
turbocharger (i.e., higher temperatures means higher heat energy, which
results in increased turbocharger boost). Consequently, engine knock
actually increases as a result of spark retard. Accordingly, the spark retard is
continuously increased until the spark retard authority is fully consumed.
SUMMARY OF THE INVENTION
[0006] Accordingly, the present invention provides an engine knock
control system for an engine including a turbocharger. The engine knock
control system includes a first module that determines octane scalars
indicative of an engine knock propensity for each cylinder of the engine
system and a second module that determines a cylinder air mass limit based
on the octane scalars. A third module limits a boost output of the
turbocharger based on the cylinder air mass limit.
[0007] In another feature, the cylinder air mass limit is determined
based on a maximum of the octane scalars.
[0008] In another feature, the cylinder air mass limit is further
determined based on an engine RPM.
[0009] In still another feature, the engine knock control system
further includes a fourth module that determines a spark retard for each
cylinder respectively based on the octane scalars.
[0010] In yet another feature, the third module limits a boost output
of the turbocharger by actuating a waste gate valve to selectively detour an
exhaust gas from entering the turbocharger.

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[0011] Further areas of applicability of the present invention will
become apparent from the detailed description provided hereinafter. It should
be understood that the detailed description and specific examples, while
indicating the preferred embodiment of the invention, are intended for
purposes of illustration only and are not intended to limit the scope of the
invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] The present invention will become more fully understood
from the detailed description and the accompanying drawings, wherein:
[0013] Figure 1 is a functional block diagram of an engine system
including a turbo charger;
[0014] Figure 2 is a graph illustrating exemplary cylinder mass air
limit traces based on octane scalar values and engine RPM;
[0015] Figure 3 is a flowchart illustrating exemplary steps executed
by the turbocharged engine knock control of the present invention; and
[0016] Figure 4 is a functional block diagram of exemplary modules
that execute the turbocharged engine knock control of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0017] The following description of the preferred embodiment is
merely exemplary in nature and is in no way intended to limit the invention, its
application, or uses. For purposes of clarity, the same reference numbers will
be used in the drawings to identify similar elements. As used herein, the term
module refers to an application specific integrated circuit (ASIC), an electronic
circuit, a processor (shared, dedicated, or group) and memory that execute
one or more software or firmware programs, a combinational logic circuit,
and/or other suitable components that provide the described functionality.

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[0018] Referring now to Figure 1, an exemplary engine system 10 is
illustrated. The engine system 10 includes an engine 12 having an intake
manifold 14 and an exhaust manifold 16. Air and fuel are mixed and the
air/fuel mixture is combusted within cylinders 18 of the engine 12. Although
the exemplary engine illustrated in Figure 1 includes 4 cylinders, it is
anticipated that the engine can include more or fewer cylinders. For example,
engines having 2, 3, 5, 6, 8, 10 and 12 cylinders are anticipated.
[0019] The engine system 10 further includes a turbocharger 20.
Exhaust gas exiting the exhaust manifold drives the turbocharger 20, which
compresses air that is drawn into the engine from atmosphere through an air
filter 22 and an air cooler 24. The compressed air is metered into the intake
manifold 14 through a throttle 26. The turbocharger 20 further includes a
waste gate 28 that is actuated to detour the exhaust gas exiting the exhaust
manifold 16. More specifically, the exhaust gas can be selectively detoured
such that it does not drive the turbocharger 20. In this manner, the amount of
boost provided by the turbocharger 20 can be regulated.
[0020] A control module 30 regulates operation of the engine
system 10 based on the turbocharged engine knock control of the present
invention. More specifically, the control module 30 regulates operation of the
throttle 26 and the waste gate 28 of the turbocharger 20 based on a plurality
of engine operating parameters. A mass air flow (MAF) sensor 32 generates
a MAF signal based on the air flow into the engine system 10 and an intake
air temperature sensor 34 generates a signal based on the temperature of the
intake air (TIA). A manifold absolute pressure (MAP) sensor 36 generates a
MAP signal and an engine temperature sensor 38 generates a signal based
on an engine temperature (TENG). TENG can be based on the temperature of a
coolant flow through the engine system 10. An engine speed sensor 40
generates an RPM signal based on the rotational speed of a crankshaft (not
shown).

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[0021] An engine knock sensor 42 is provided and can include any
vibration sensor or other sensor known in the art to produce a signal based on
a knock related engine parameter. For example, a sensor that senses engine
vibration within a predetermined frequency range is anticipated. A knock
count CKNOCK is generated based on the signal of the engine knock sensor 42,
and includes a counter value that is periodically cleared and that is
incremented upon identification of a sensed knock event or condition. It is
also anticipated that a knock processor (not shown) can be implemented to
reduce signal noise.
[0022] The turbocharged engine knock control of the present
invention is partially based on the engine knock control disclosed in U.S.
Patent No. 5,560,337, entitled Knock Control Using Fuzzy Logic, and issued
on October 1, 1996, the disclosure of which is expressly incorporated herein
by reference. More specifically, the turbocharged engine knock control
determines a knock propensity value or octane scalar for each cylinder 18 of
the engine 12. The octane scalar varies between 0 and 1. A value of 0
indicates no propensity to knock and a value of 1 indicates a very high
propensity to knock. A maximum air mass per cylinder is determined based
on the octane scalars and the maximum boost of the turbocharger 20 is
limited such that the maximum air mass per cylinder is not exceeded. In this
manner, turbocharger boost is limited to inhibit increased engine knock, which
would otherwise result from increased boost. Additionally, spark retard
authority is maintained at usable levels.
[0023] The turbocharged engine knock control monitors engine
operating parameters including, but not limited to, TIA, MAP, TENG, CKNOCK and
RPM. A base spark timing is determined based on MAP and RPM. For
example, the base spark timing can be determined from a look-up table based
on MAP and RPM. A retarded spark timing is subsequently determined
based on the octane scalar.

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[0024] Although a brief description of calculation of the octane
scalar is provided herein, a more detailed description is provided in U.S.
Patent Np. 5,560,337, described above. The octane scalar is determined as
the ratio between a numerator value (NUM) and a denominator value
(DENOM). NUM and DENOM are determined based on a plurality of
membership functions that are consistent with fuzzy logic control, wherein the
above-described operating parameters are sub-divided into a plurality of
categories. For example, TENG is subdivided into the categories of low temp,
high temp and not low temp, MAP is subdivided into low pressure and high
pressure, and RPM is sub-divided into low speed and high speed.
[0025] The membership functions are applied to a knowledge rule
base to determine a set of associated truths after determining membership
function output values. The rules forming the rule base are determined in an
analysis of the impact of the membership functions on engine knock
propensity. After determining the truths, NUM and DENOM are used to
compute the octane scalar. More specifically, the octane scalar is computed
as a weighted sum of NUM and DENOM, each of which is summed over each
truth. NUM and DENOM are calculated based on the following equations:
NUM = NUM+TRUTH(n)*POS(n)*WEIGHT(n)
DENOM = DENOM+TRUTH(n)*WEIGHT(n)
where n is the truth number, POS is a position value and WEIGHT is a
weighting value. The position values may be determined in a calibration step
as the extent that the associated truth indicates engine knock propensity. The
weight values are used to weight the truths with respect to each other, to
reflect any variance in the degree by which the rules indicate a knock
propensity.
[0026] Once the octane scalar is calculated for a particular cylinder,
the retarded spark timing is determined for that cylinder based thereon.
Further, the turbocharged engine spark control determines a cylinder air mass
limit as a function of the maximum octane scalar value for each of the
cylinders and the engine RPM. More specifically, a look-up table can be

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implemented using the maximum octane scalar value and engine RPM as
inputs. The graph of Figure 2 illustrates exemplary cylinder mass air limit
traces based on the octane scalar value and the engine RPM. The boost
provided by the turbocharger 20 is limited based on the cylinder air mass limit.
In this manner, the pressure decreases the propensity for engine knock
thereby reducing the need to retard the spark timing.
[0027] Referring now to Figure 3, exemplary steps executed by the
turbocharged engine knock control will be described in detail. In step 200,
control monitors the engine operating parameters including, but not limited to,
TIA, MAP, TENG, CKNOCK and RPM. In step 202, control calculates the octane
scalar for each cylinder. Control determines the spark timing for each cylinder
based on its corresponding octane scalar in step 204. In step 206, control
determines the cylinder mass air limit based on the maximum octane scalar
value and the engine RPM. In step 208, control limits the maximum
turbocharger boost based on the cylinder air mass limit and control ends.
[0028] Referring now to Figure 4, exemplary modules that execute
the turbocharged engine knock control will be described in detail. The
exemplary modules include an octane scalar determining module 300, a spark
retard calculating module 302, an engine ignition control module 304, a
cylinder air mass limit determining module 306 and a turbocharger control
module 308. The octane scalar determining module 300 determines the
octane scalar based on TIA, MAP, TENG, CKNOCK and RPM. The spark retard
calculating module 302 determines the amount of spark retard based on the
octane scalar and the engine ignition control module 304 generates a spark
control signal based on the amount of spark retard.
[0029] The cylinder air mass limit determining module 306
determines the cylinder mass air limit based on the octane scalar and the
engine RPM. The turbocharger control module 308 generates a boost control
signal based on the cylinder air limit. More specifically, the waste gate 28 is
actuated based on the boost control signal to limit the boost output of the
turbocharger to the cylinder mass air limit.

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[0030] Those skilled in the art can now appreciate from the
foregoing description that the broad teachings of the present invention can be
implemented in a variety of forms. Therefore, while this invention has been
described in connection with particular examples thereof, the true scope of the
invention should not be so limited since other modifications will become
apparent to the skilled practitioner upon a study of the drawings, the
specification and the following claims.

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CLAIMS
What is claimed is:
1. An engine knock control system for an engine including a turbocharger,
comprising:
a first module that determines octane scalars indicative of an engine
knock propensity for each cylinder of said engine system;
a second module that determines a cylinder air mass limit based on
said octane scalars; and
a third module that limits a boost output of said turbocharger based on
said cylinder air mass limit.
2. The engine knock control system of claim 1 wherein said cylinder air
mass limit is determined based on a maximum of said octane scalars.
3. The engine knock control system of claim 1 wherein said cylinder air
mass limit is further determined based on an engine RPM.
4. The engine knock control system of claim 1 further comprising a fourth
module that determines a spark retard for each cylinder respectively based on
said octane scalars.
5. The engine knock control system of claim 1 wherein said third module
limits a boost output of said turbocharger by actuating a waste gate valve to
selectively detour an exhaust gas from entering said turbocharger.
6. A method of controlling engine knock in an engine system including a
turbocharger, comprising:
determining octane scalars indicative of an engine knock propensity for
each cylinder of said engine system;
determining a cylinder air mass limit based on said octane scalars; and

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limiting a boost output of said turbocharger based on said cylinder air
mass limit.
7. The method of claim 6 wherein said cylinder air mass limit is
determined based on a maximum of said octane scalars.
8. The method of claim 6 wherein said cylinder air mass limit is further
determined based on an engine RPM.
9. The method of claim 6 further comprising determining a spark retard for
each cylinder respectively based on said octane scalars.
10. The method of claim 6 wherein said step of limiting a boost output of
said turbocharger includes actuating a waste gate valve to selectively detour
an exhaust gas from entering said turbocharger.
11. A method of controlling engine knock in an engine system including a
turbocharger, comprising:
monitoring engine operating parameters;
determining octane scalars indicative of an engine knock propensity for
each cylinder of said engine system based on said engine operating
parameters;
determining a cylinder air mass limit based on said octane scalars;
adjusting a spark timing to mitigate engine knock; and
limiting a boost output of said turbocharger based on said cylinder air
mass limit.
12. The method of claim 11 wherein said cylinder air mass limit is
determined based on a maximum of said octane scalars.

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13. The method of claim 11 wherein said cylinder air mass limit is further
determined based on an engine RPM.
14. The method of claim 11 said step of adjusting a spark timing comprises
determining a spark retard for each cylinder respectively based on said
octane scalars.
15. The method of claim 11 wherein said step of limiting a boost output of
said turbocharger includes actuating a waste gate valve to selectively detour
an exhaust gas from entering said turbocharger.

An engine knock control system for an engine having a turbocharger
includes a first module that determines octane scalars indicative of an engine
knock propensity for each cylinder of the engine system and a second module
that determines a cylinder air mass limit based on the octane scalars. A third
module limits a boost output of the turbocharger based on the cylinder air
mass limit.